The background of the invention is set forth in two parts: the field of the invention and the description of related art.
1. Field of the Invention
This invention relates to a method and apparatus for wastewater flow monitoring. In particular, it relates to wastewater flow metering and sampling.
2. Description of Related Art
The invention disclosed herein provides improvements to the state of the art and particularly to the inventions disclosed in U.S. Pat. No. 4,799,388 by Hunter, Jan. 24, 1989, entitled "Apparatus and Technique for Metering Liquid Flow"; U.S. Pat. No. 4,896,542 by Hunter Jan. 30, 1990, entitled "Portable Wastewater Flow Meter"; and U.S. Pat. No. 5,199,306 by Hunter, Apr. 6, 1993, entitled "Method and Apparatus for Metering Flow in Closed Conduits that Surcharge". The disclosure of the aforementioned U.S. patents are incorporated by reference herein as if fully set forth.
Those patents disclose a variety of primary flow elements and secondary flow elements. In some embodiments, the primary flow elements comprise constrictions configured to cause simultaneous filling of the constriction and the upstream pipe upon increasing flow rate. In other disclosed embodiments, the primary flow elements comprise constrictions configured to cause filling of the constrictions and/or the upstream pipe before the modular limit of the device is reached. The disclosed secondary flow elements utilize a variety of means to transmit and sense the level and pressure changes caused by the primary flow elements.
A variety of commercially-available devices may be used for wastewater monitoring. One example is the Sigma 950 Series Open Channel Flow Meter manufactured by American Sigma. It is a secondary element that can be used with such primary elements as weirs, flumes, and nozzles. A rain gauge and an automatic sampler can be connected to the secondary element. Data can be downloaded from this secondary element via a hand-held memory module, a telephone modem, or a personal computer.
Another example is the Isco 3200 Series Open Channel Flow Meter manufactured by Isco, Inc. Data can be downloaded from this secondary element via a laptop computer, a short haul modem, a telephone modem, or a data switch.
Some of these flowmeters, as well as flowmeters manufactured by Marsh McBirney, Inc. and Stevens Inc. measure flow rate by directly measuring velocity and depth. Thus, no primary element is required.
The Streamline 800SL Portable Liquid Sampler manufactured by American Sigma is an example of a portable sampler. It is described in U.S. Pat. No. 4,660,607, the disclosure of which is incorporated herein as if fully set forth. Other examples are the Isco Model 6000 Sampler and the Isco 3700 Series Portable Wastewater Samplers manufactured by Isco, Inc.
Other background material is presented in a report entitled "Distributed Unattended Storm Water Discharge Monitoring--Phase I Final Technical Report", dated October 1994, by Yellowstone Environmental Science, Inc., 320 S. Willson Ave., Bozeman, Mont. 59715, at the e-mail address 74203.3640@compuserv.com. The disclosure in that report is incorporated by reference herein as if fully set forth.
Limitations of prior art systems include the need for hard-wired connections among system components. For example, in order to interrogate a secondary unit that is installed in a sewer manhole, the heavy manhole cover must be removed and an RS-232 cable connected between the secondary element and the portable computer being used to interrogate the secondary element. Prior art systems are also limited in that accurate flow metering in closed conduits that surcharge is not possible and a separate rain gauge must be hard-wire connected to each secondary element.